<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>伪元素</title>
    <style type="text/css">
      li {
        list-style: none;
      }
      li::before {
        content: "*";
      }
    </style>
  </head>
  <body>
    <ul>
      <li>我是第一</li>
      <li>我是第二</li>
      <li>我是第三</li>
      <li>我是第四</li>
    </ul>
  </body>
</html>
